Vehicle body structure

ABSTRACT

In a vehicle body structure including a pair of side sills ( 2 ) and a battery case ( 51 ) joined to the side sills via respective brackets ( 56 ), each side sill includes an outer panel ( 21 ), an inner panel ( 22 ) defining a closed cross section structure jointly with the outer panel, a first stiffener ( 25 ) extending in the fore and aft direction in a space defined between the outer panel and the inner panel and having a lower edge joined to the lower edges of the outer panel and the inner panel, and a second stiffener ( 26 ) formed as a channel member extending in the fore and aft direction and having an open side facing in the inboard direction, the second stiffener having an upper edge and a lower edge attached to an outboard side of the first stiffener.

TECHNICAL FIELD

The present invention relates to a vehicle body structure, and inparticular to a structure of a lower side part of a vehicle body.

BACKGROUND OF THE INVENTION

In a known vehicle body structure, a battery unit is positioned betweena pair of side sills extending in the fore and aft direction on eitherlower side part of a vehicle body (see JP2014-226958A, for example). Insuch a vehicle body structure, in order to minimize the deformation ofthe battery unit at the time of a side crash, the part of the vehiclebody associated with the side sills is required to be able tosufficiently absorb the impact load of the side crash. According to theproposal disclosed in JP2006-264476A, each side sill is formed by aninner panel and an outer panel which are joined to each other so as toform a hollow structure. This hollow structure is reinforced by a firststiffener interposed between the inner panel and the outer panel, and asecond stiffener attached to the outboard side of the first stiffener.The second stiffener is made of an aluminum alloy, and defines a hollowstructure in cooperation with the first stiffener. At the time of a sidecrash, the second stiffener undergoes a deformation between the outerpanel and the first stiffener which are also deformed.

The capacity to absorb the impact load of a side crash depends on theload energy absorbing capability or the amount of deformation of thesecond stiffener. It is therefore crucial to ensure the second stiffenerto deform in a predictable manner by limiting the inboard displacementof the second stiffener. In other words, a certain structure is requiredto transmit a reaction force to the second stiffener from the inboardside against the impact load applied from the outboard side.

BRIEF SUMMARY OF THE INVENTION

In view of such a problem of the prior art, a primary object of thepresent invention is to provide a vehicle body structure provided with apair of side sills that can improve the capacity of the side sills toabsorb the energy of an impact load of a side crash.

To achieve such an object, the present invention provides a vehicle bodystructure (1), comprising: a pair of side sills (2) extending in a foreand aft direction along either lower side part of a vehicle body; a pairof brackets (56) joined to inboard sides of the respective side sills;and a battery case (51) joined to the brackets and receiving a batterypack therein, wherein each side sill includes: an outer panel (21)formed as a channel member extending in the fore and aft direction andhaving an open side facing in an inboard direction; an inner panel (22)formed as a channel member extending in the fore and aft direction andhaving an open side facing in an outboard direction, the outer panel andthe inner panel being joined to each other at upper and lower edgesthereof; a first stiffener (25) extending in the fore and aft directionin a space defined between the outer panel and the inner panel andhaving a lower edge joined to the lower edges of the outer panel and theinner panel; and a second stiffener (26) formed as a channel memberextending in the fore and aft direction and having an open side facingin the inboard direction, the second stiffener having an upper edge anda lower edge attached to an outboard side of the first stiffener.

Thus, the second stiffener and the first stiffener are connected to thebattery case via the inner panel and the bracket. Therefore, at the timeof a side crash, the second stiffener and the first stiffener receive areaction force from the battery case via the inner panel and thebracket. As a result, the second stiffener and the first stiffener arecaused to deform in a reliable manner so that the side sill can absorbthe energy of the impact load in an efficient manner.

Preferably, the outer panel includes an outer lower wall (21A) extendingtransversely, an outer vertical wall (21B) extending upward from anoutboard edge of the outer lower wall, an outer upper wall (21C)extending in the inboard direction from an upper edge of the outervertical wall (21B), an outer lower flange (21D) extending downward froman inboard edge of the outer lower wall, and an outer upper flange (21E)extending upward from an inboard edge of the outer upper wall (21C).Preferably, in addition, the inner panel includes an inner lower wall(22A) extending transversely, an inner vertical wall (22B) extendingupward from an inboard edge of the inner lower wall, an inner upper wall(22C) extending in the outboard direction from an upper edge of theinner vertical wall, an inner lower flange (22D) extending downward froman outboard edge of the inner lower wall and joined to the outer lowerflange, and an inner upper flange (22E) extending upward from anoutboard edge of the inner upper wall and joined to the outer upperflange, and the second stiffener includes a second stiffener lowerflange (26A) located on a lower part of the open side of the secondstiffener (26) and joined to an outboard side of a lower edge of thefirst stiffener (25), a second stiffener lower wall (26B) extending inthe outboard direction from an upper edge of the second stiffener lowerflange, a second stiffener vertical wall (26C) extending upward from anoutboard edge of the second stiffener lower wall, a second stiffenerupper wall (26D) extending in the inboard direction from an upper edgeof the second stiffener vertical wall, and a second stiffener upperflange (26E) extending upward from an inboard edge of the secondstiffener upper wall and joined to an outboard side of an upper edge ofthe first stiffener, an outboard edge of the inner lower wall (22A)being offset upward from an inboard edge of the outer lower wall (21A),and transversely opposing an inboard edge of the second stiffener lowerwall (26B) via the first stiffener (25).

Since the outboard edge of the inner lower wall transversely opposes theinboard edge of the second stiffener lower wall, the inner lower wall isable to efficiently transmit a reaction force to the second stiffener inan efficient manner.

Preferably, the battery case includes a lower case (52) having anopening facing upward and a flange (52B) extending along a periphery ofthe opening, and an upper case (53) closing the opening of the lowercase and having a periphery joined to the flange of the lower case, thebattery case being joined to the brackets at the flange of the lowercase.

Since the battery case is joined to the brackets via the flanges of thelower case and the upper case having a relatively high stiffness, thebattery case is enabled to transmit a reaction force to the side sillsvia the brackets without substantially deforming.

Preferably, each bracket includes a vertical wall portion (56A)extending downward from the flange of the lower case, and a transversewall portion (56B) extending from a lower end of the vertical wallportion to under the inner lower wall to be joined to the inner lowerwall.

Thereby, an end of each bracket can be joined to a lower part of theinner panel located adjacent to the lower end of the first stiffenerwhile the bracket is positioned transversely between the battery caseand the side sill.

Preferably, each bracket has a lower rigidity than the lower caseagainst a transverse loading.

Since the bracket deforms before the lower case deforms, and absorbs theenergy of the transverse loading, the deformation of the lower case canbe minimized.

Preferably, the inner lower wall is provided with a plurality of beads(22J) each extending in a transverse direction.

Thereby, by increasing the stiffness of the inner lower wall against atransverse loading, the amount of energy that can be absorbed by theinner lower wall can be increased. Also, at the time of a side crash,the inner lower wall can transmit a reaction force in a reliable manner.

Preferably, the vehicle body structure further comprises a thirdstiffener (27) extending in the fore and aft direction in a spacedefined between the inner lower wall and the inner upper wall, and in atransverse direction to have an outboard edge joined to the firststiffener and an inboard edge joined to the inner vertical wall.

Thereby, the inner panel is enabled to transmit a reaction force to thefirst stiffener and the second stiffener via the third stiffener.

Preferably, the outboard edge of the third stiffener and the upper edgeof the second stiffener transversely oppose each other via the firststiffener.

Thereby, the third stiffener is enabled to transmit a reaction force tothe second stiffener in an efficient manner at the time of a side crash.

Preferably, the vehicle body structure further comprises: a floor panel(18) having a vertically facing surface and attached to upper sides ofthe inner upper walls along respective lateral side edges thereof; and apair of side members (12) each having an outboard edge attached to aninboard side of the inner vertical wall and an inboard edge attached alower surface of the floor panel.

According to this arrangement, the second stiffener and the firststiffener are connected to the floor panel via the third stiffener, theinner panel and the side member so that the second stiffener and thefirst stiffener can receive the reaction force from the floor panel viathe side member, the inner panel and the third stiffener, and can deformin a reliable manner.

Preferably, the vehicle body structure further comprises a cross memberextending transversely and attached to the lower surface of the floorpanel, two transverse ends of the cross member being joined to therespective side members.

Since the side members are connected to the cross member, thedisplacement of the side members at the time of a side crash can becontrolled so that the side members are enabled to transmit a reactionforce to the inner panel, the third stiffener, the first stiffener andthe second stiffener.

Preferably, a lower edge of the first stiffener (25) is provided with aplurality of notches (58) extending upward, and the outer lower flange(21D), the second stiffener lower flange (26A), a lower edge of thefirst stiffener (25), and the inner lower flange (22D) are laid over oneanother, wherein the outer lower flange (21D), the second stiffenerlower flange (26A), and the inner lower flange (22D) are integrallywelded to one another at positions corresponding to the notches.

Thereby, the outer lower flange, the second stiffener lower flange andthe lower edge of the first stiffener and the inner lower flange can beintegrally joined to one another.

Preferably, the vehicle body structure further comprises a door sliderail provided between the inner panel and the outer panel, and locatedabove the first stiffener, the door slide rail being configured toslidably guide a lower end of a slide door.

Thereby, the side sill having the door slide rail incorporated thereincan be given with an improved capability to absorb the energy of a sidecrash load.

Thus, the present invention provides a vehicle body structure includinga pair of side sills that can improve the capacity of the side sills toabsorb the energy of an impact load of a side crash.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary perspective view of a vehicle body structureaccording to an embodiment of the present invention as viewed from theright side;

FIG. 2 is a bottom view of the vehicle body structure with a batteryunit and brackets therefor being omitted from illustration;

FIG. 3 is a sectional view taken along the line III-III of FIG. 1;

FIG. 4 is a sectional view taken along line IV-IV of FIG. 1;

FIG. 5 is an exploded perspective view of a side sill;

FIG. 6 is a sectional view similar to FIG. 3 in an early stage (firststage) of deformation;

FIG. 7 is a sectional view similar to FIG. 3 in an intermediate stage(second stage) of deformation;

FIG. 8 is a sectional view similar to FIG. 3 in a final stage (thirdstage) of deformation;

FIG. 9 is a sectional view similar to FIG. 8 of a vehicle body structuregiven as an example for comparison; and

FIG. 10 is a graph showing the deformation history of a battery casewith respect to a displacement of an object colliding with the vehiclebody structure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Now the present invention is described in the following in more detailin terms of a concrete embodiment with reference to the appendeddrawings. In the following description, the various components of thevehicle body are made of metallic material such as steel sheet unlessotherwise specified. The connecting, joining, bonding and attaching asused in the following disclosure may include various modes of connectionsuch as welding, stir welding, fastening (rivets, screws, clips, etc.)and adhesive bonding. Since the vehicle body is generally symmetricabout a central axial line extending in the fore and aft direction, onlyone side of the vehicle may be mentioned in the following description toavoid redundancy.

As shown in FIG. 1, a pair of side sills 2 extending in the fore and aftdirection are provided on either lower side part of a vehicle bodystructure 1 of a minivan type vehicle. A front end part of the side sill2 is connected to a lower end of an A pillar 3 extending vertically, andan intermediate part of the side sill 2 with respect to the fore and aftdirection is connected to a lower end of a B pillar 4 also extendingvertically. A rear end part of the side sill 2 is connected to the lowerend of a C pillar 5 also extending vertically. A front door opening 7 isdefined between the A pillar 3 and the B pillar 4, and a rear dooropening 8 is defined between the B pillar 4 and the C pillar 5. Thefront door opening 7 is fitted with a swing door (not shown in thedrawings), and the rear door opening 8 is fitted with a slide door (notshown in the drawings).

As shown in FIG. 2, front parts of the side sills 2 are connected toeach other by a front cross member 11 extending laterally. A pair ofside members 12 are provided on the inner sides of the intermediateregions of the respective side sills 2 with respect to the fore and aftdirection of the vehicle body. The side members 12 are connected to eachother by the intermediate cross member 13 extending laterally. Morespecifically, the intermediate parts of the side sills 2 are connectedto each other by the intermediate cross member 13 via the respectiveside members 12.

A rear side frame 15 is attached to the inner side of a rear end part ofeach side sill 2, and extends obliquely inward and rearward in a frontpart thereof, and extends linearly rearward in a remaining part thereof.The two rear side frames 15 are connected to each other by three rearcross members 16 extending laterally in a mutually spaced apartrelationship.

A front floor panel 18 is attached to the upper surfaces of the frontcross member 11 and the intermediate cross member 13. The front floorpanel 18 extends substantially horizontally, and are joined to the sidesills 2 along the respective side edges thereof. A rear floor panel 19is attached to the upper surfaces of the side frames 15 and the rearcross members 16. A rear floor panel 19 is joined to the rear edge ofthe front floor panel 18 at the front edge thereof. The front floorpanel 18 and the rear floor panel 19 jointly form the floor of thepassenger compartment.

As mentioned earlier, the vehicle body is substantially symmetric aboutthe center line extending in the fore and aft direction. Only the lowerleft part of the vehicle body structure 1 is described in the followingto avoid redundancy.

As shown in FIGS. 3 to 5, the side sill 2 includes an outer panel 21positioned on the outboard side, and an inner panel 22 positioned on theinboard side. The outer panel 21 is formed as a channel member having anopen side facing in the inboard direction, and extending in the fore andaft direction. The inner panel 22 is also formed as a channel memberhaving an open side facing in the outboard direction, and extending inthe fore and aft direction, and is joined to the outer panel 21 alongthe upper edge and the lower edge thereof. The outer panel 21 and theinner panel 22 jointly form a closed cross section structure 23.Preferably, the outer panel 21 and the inner panel 22 are formed of hightensile steel.

More specifically, the outer panel 21 includes a lower wall 21Aextending laterally, a vertical wall 21B extending upward from theoutboard edge of the lower wall 21A, an upper wall 21C extending in theinboard direction from the upper edge of the vertical wall 21B, a lowerflange 21D extending downward from the inboard edge of the lower wall21A, and an upper flange 21E extending upward from the inboard edge ofthe upper wall 21C. The inner panel 22 includes a lower wall 22Aextending laterally, a vertical wall 22B extending upward from theinboard edge of the lower wall 22A, an upper wall 22C extending in theoutboard direction from the upper edge of the vertical wall 22B, a lowerflange 22D extending downward from the outboard edge of the lower wall22A, and an upper flange 22E extending upward from the outboard edge ofthe upper wall 22C. The upper flange 21E of the outer panel 21 and theupper flange 22E of the inner panel 22 are joined to each other, and thelower flange 21D of the outer panel 21 and the lower flange 22D of theinner panel 22 are joined to each other.

The vertical wall 21B of the outer panel 21 includes a vertical wallupper portion 21F extending substantially linearly downward from theoutboard edge of the upper wall 21C, and a vertical wall lower portion21G bulging in the outboard direction.

The vertical wall 22B of the inner panel 22 includes a vertical wallupper portion 22F extending substantially linearly downward from theinboard edge of the upper wall 22C, and a vertical wall lower portion22G extending substantially linearly upward from the inboard edge of thelower wall 22A and offset from the vertical wall upper portion 22F inthe outboard direction. The region of the vertical wall 22B located atthe boundary between the vertical wall upper portion 22F and thevertical wall lower portion 22G is formed as a vertical wallintermediate portion 22H that is slanted in the inboard direction as onemoves upward.

The lower flange 22D of the inner panel 22 is slightly offset upwardfrom the lower flange 21D of the outer panel 21, and the outboard edgeof the lower wall 22A of the inner panel 22 is offset upwardly withrespect to the inboard edge of the lower wall 21A of the outer panel 21.The lower wall 22A of the inner panel 22 is provided with a plurality ofbeads 22J arranged in the fore and aft direction and each elongated inthe lateral direction. The beads 22J increase the stiffness of the lowerwall 22A against a laterally applied force, and absorb a large amount ofenergy when deformed under a lateral force. The beads 22J protrudeupward from the lower wall 22A in the illustrated embodiment, but mayalso protrude downward if desired.

The closed cross section structure 23 formed by the outer panel 21 andthe inner panel 22 is internally provided with a first stiffener 25, asecond stiffener 26, and a third stiffener 27. The first stiffener 25 isformed as a planar plate-shaped member extending vertically and having amajor plane facing laterally. The lower edge of the first stiffener 25is interposed between the lower flange 21D of the outer panel 21 and thelower flange 22D of the inner panel 22. The upper edge of the firststiffener 25 extends to a substantially same height as the vertical wallintermediate portion 22H of the inner panel 22.

The second stiffener 26 is formed as a channel member having an openside facing in the inboard direction, and extending in the fore and aftdirection. The second stiffener 26 includes a lower flange 26A locatedon the lower part of the open side of the second stiffener 26 and joinedto the outboard side of the lower edge of the first stiffener 25, alower wall 26B extending in the outboard direction from the upper edgeof the lower flange 26A, a vertical wall 26C extending upward from theoutboard edge of the lower wall 26B, an upper wall 26D extending in theinboard direction from the upper edge of the vertical wall 26C, and anupper flange 26E extending upward from the inboard edge of the upperwall 26D and joined to the outboard side of the upper edge of the firststiffener 25. The second stiffener 26 and the first stiffener 25 jointlyform a closed cross section structure 29.

The lower flange 21D of the outer panel 21, the lower flange 26A of thesecond stiffener 26, the lower edge of the first stiffener 25, and thelower flange 22D of the inner panel 22 are laid over one another in thatorder in the inboard direction. As shown in FIG. 5, the lower edge ofthe first stiffener 25 is provided with a plurality of notches 58extending upward. The lower flange 21D of the outer panel 21, the lowerflange 26A of the second stiffener 26, and the lower flange 22D of theinner panel 22 are integrally welded at positions corresponding to thenotches 58. More specifically, the lower flange 21D of the outer panel21, the lower flange 26A of the second stiffener 26, and the lowerflange 22D of the inner panel 22 are welded to one another, and thelower edge of the first stiffener 25 is interposed between the lowerflange 26A of the second stiffener 26 and the lower flange 22D of theinner panel 22. Owing to this arrangement, the lower flange 21D of theouter panel 21, the lower flange 26A of the second stiffener 26, thelower edge of the first stiffener 25, and the lower flange 22D of theinner panel 22 are integrally joined to one another. In an alternativeembodiment, the notches 58 are provided in the lower flange 26A of thesecond stiffener 26 instead of the lower edge of the first stiffener 25.

As shown in FIG. 3, the upper end of the upper flange 26E of the secondstiffener 26 is positioned at the same height as the upper end of thefirst stiffener 25. An upper part of the lower flange 26A of the secondstiffener 26 protrudes above the lower flange 21D of the outer panel 21.As a result, the lower wall 26B of the second stiffener 26 is positionedabove the lower wall 21A of the outer panel 21 with a gap definedtherebetween. The inboard edge of the lower wall 26B of the secondstiffener 26 is positioned so as to oppose the outboard edge of thelower wall 22A of the inner panel 22 via the first stiffener 25. Inother words, the inboard edge of the lower wall 26B of the secondstiffener 26 and the outboard edge of the lower wall 22A of the innerpanel 22 are positioned at a substantially same height.

The lower wall 26B and the upper wall 26D of the second stiffener 26 areinclined so as to come toward each other as one moves in the outboarddirection. At least one of the lower wall 26B and the upper wall 26D isformed with at least one bending portion 31 bent inward of the channelshape (inward of the closed cross section structure 29) defined by thesecond stiffener 26. The bending portion 31 may be provided with aconvex shape facing toward the interior of the closed cross sectionstructure 29 in cross sectional view. In the illustrated embodiment,such a bending portion 31 is provided in each of the lower wall 26B andthe upper wall 26D of the second stiffener 26.

As shown in FIG. 5, the lower wall 26B and the upper wall 26D of thesecond stiffener 26 are provided with a plurality of beads 26F arrangedin the fore and aft direction and each extending in the lateraldirection. The beads 26F increase the stiffness of the second stiffener26 against a laterally directed loading, and increase the amount ofenergy that can be absorbed when deformed in the lateral direction. Thebeads 26F may either protrude upward or downward from the lower wall 26Band the upper wall 26D. The beads 26F are absent in the bending portions31. In other words, the beads 26F are provided so as not to cross thebending portions 31.

The third stiffener 27 includes a transverse wall 27A extending both inthe fore and aft direction and in the lateral direction, an outer flange27B extending upward from the outboard edge of the transverse wall 27A,and an inner flange 27C extending upward and in the inboard directionfrom the inboard edge of the transverse wall 27A. The third stiffener 27is joined to the first stiffener 25 at the outer flange 27B thereoflocated on the outboard edge of the third stiffener 27, and is joined tothe vertical wall intermediate portion 22H of the inner panel 22 at theinner flange 27C thereof located on the inboard edge of the thirdstiffener 27. As shown in FIG. 5, the transverse wall 27A is providedwith a plurality of beads 27D arranged in the fore and aft direction andeach extending in the lateral direction. The beads 27D increase thestiffness of the third stiffener 27 against a laterally directedloading, and increases the amount of energy that can be absorbed whendeformed in the lateral direction. The beads 27D may protrude eitherupward or downward from the transverse wall 27A.

As shown in FIG. 3, the outer flange 27B of the third stiffener 27 andthe upper flange 26E of the second stiffener 26 laterally oppose eachother via the first stiffener 25. In particular, the lower edges of theupper flange 26E of the second stiffener 26 and the outer flange 27B ofthe third stiffener 27 are substantially aligned with each other, orsubstantially at a same height. As a result, the inboard end of theupper wall 26D of the second stiffener 26 opposes the outboard end ofthe transverse wall 27A of the third stiffener 27, or are at asubstantially same height.

As shown in FIG. 4, a door slide rail 35 extending in the fore and aftdirection for slidably supporting a lower arm (not shown) extending froma lower end of a slide door is provided in a part of the vehicle bodyinboard of the outer panel 21 and the inner panel 22 and above the firststiffener 25. The door slide rail 35 is attached to the lower surface ofthe upper wall of a channel shaped rail case 36 having an open sidefacing in the outboard direction. An outer opening 37 facing in theoutboard direction and extending in the fore and aft direction is formedin the vertical wall upper portion 21F of the outer panel 21. Theopening edges or the outboard edges of the rail case 36 are joined tothe opening edges of the outer opening 37. The lower arm of the slidedoor extends from the lower end of a slide door into the rail case 36,and the free end of the lower arm is supported by the door slide rail35.

As shown in FIG. 1, FIG. 2 and FIG. 4, the rail case 36 is provided witha bulging portion 36A bulging in the inboard direction in the front endpart thereof. The bulging portion 36A progressively bulges in theinboard direction toward the front so that the rail case 36 in effectprogressively increases in depth (as measured in the lateral direction)toward the front. The door slide rail 35 is curved in the inboarddirection in a front end part thereof corresponding to the bulgingportion 36A. An inner opening 38 is passed through the vertical wallupper portion 22F of the inner panel 22 and extends in the fore and aftdirection. The bulging portion 36A of the rail case 36 passes throughthe inner opening 38 and projects to a position more inboard than thevertical wall 22B. The front end of the door slide rail 35 is curved inthe inboard direction so the slide door is pulled in the inboarddirection in the closed position (front most position).

As shown in FIG. 2, a middle part of the side member 12 protrudes in theinboard direction in plan view in an arcuate manner. As shown in FIG. 3,the side member 12 includes an outer edge joining portion 12A joined toan inboard side face of the vertical wall intermediate portion 22H ofthe inner panel 22, a first inclined portion 12B extending obliquely inan inboard and upward direction from the outer edge joining portion 12A,a second inclined portion 12C extending in an inboard and upwarddirection from the inboard edge of the first inclined portion 12B at anangle relative to the horizontal plane greater than that of the firstinclined portion 12B, and an inner edge joining portion 12D extending inthe horizontal direction from the inboard edge of the second inclinedportion 12C and joined to the lower surface of the front floor panel 18.In an alternative embodiment of the present invention, the firstinclined portion 12B extends substantially horizontally.

The side member 12 forms a closed cross section structure 41 incooperation with the front floor panel 18 and the inner panel 22. Theprotruding end of the bulging portion 36A of the rail case 36 extendsinto the closed cross section structure 41 formed by the side member 12.The outboard end of the intermediate cross member 13 is joined to theinboard side of the second inclined portion 12C of the side member 12.

A battery unit 50 is positioned under the front floor panel 18 andbetween the left and right side sills 2. The battery unit 50 includes abattery case 51, a battery pack (not shown) accommodated in the batterycase 51, and a control unit (not shown) for controlling the charging anddischarging of the battery pack. The battery case 51 is formed bycombining a lower case 52 and an upper case 53.

The lower case 52 has a box-shaped main body 52A having an upper openingand a flange 52B extending along the opening edge of the upper openingof the main body 52A. The main body 52A is formed as a shallowrectangular pan. The flange 52B extends horizontally and along theentire periphery of the opening edge of the upper opening of the mainbody 52A.

The upper case 53 has a main body 53A having a lower opening and aflange 53B extending along the opening edge of the lower opening of themain body 53A. The main body 53A is formed as a shallow rectangular pan.The flange 53B extends horizontally along the opening edge of the loweropening of the main body 53A. The lower case 52 and the upper case 53are joined to each other at the flange 52B and the flange 53B.

The battery case 51 is attached to the inner panel 22 of each side sill2 by a bracket 56 extending in the fore and aft direction. The bracket56 has a vertical wall portion 56A extending vertically and fastened tothe lower surface of the flange 52B of the lower case 52 with threadedbolts, and a transverse wall portion 56B extending in the outboarddirection from the lower end of the vertical wall portion 56A under thelower wall 22A and fastened to the lower surface of the lower wall 22Awith threaded bolts. A support piece 56C extends in the inboarddirection from the lower end of the vertical wall portion 56A andsupports the bottom portion of the main body 52A from below.

The vertical wall portion 56A of the bracket 56 laterally opposes thevertical wall lower portion 22G of the inner panel 22 with a gap definedtherebetween, and the upper end thereof is positioned at approximately asame height as the upper end of the vertical wall lower portion 22G. Asa result, the flanges 52B and 53B of the battery case 51 are arranged ata substantially same height as the inner flange 27C provided at theinboard edge of the third stiffener 27. The flanges 52B and 53B of thebattery case 51 are positioned under the side member 12 with a gapdefined therebetween. In order to avoid interference with the sidemember 12, the main body 53A of the upper case 53 is provided with anarrower width as measured in the transverse direction than the mainbody 52A of the lower case 52.

The bracket 56 is made of an extruded aluminum alloy, and is providedwith a hollow structure. It is preferable that the bracket 56 has alower rigidity than the battery case 51 with respect to the loaddirected in the lateral direction.

The effect of the vehicle body structure 1 according to the embodimentconfigured as described above will be discussed in the following. Inthis vehicle body structure 1, the upper end of the second stiffener 26is connected to the front floor panel 18 and the intermediate crossmember 13 via the upper end of the first stiffener 25, the thirdstiffener 27, the vertical wall intermediate portion 22H of the innerpanel 22 and the side member 12. Therefore, the load applied to an upperpart of the second stiffener 26 at the time of a side crash istransmitted to the front floor panel 18 and the intermediate crossmember 13 via the upper end of the first stiffener 25, the thirdstiffener 27, the vertical wall intermediate portion 22H of the innerpanel 22, and the side member 12. This load transmission path isreferred to as a first load transmission path. In other words, thesecond stiffener 26 can transmit a reaction force from the front floorpanel 18 and the intermediate cross member 13 via the first loadtransmission path at the time of a side crash.

The lower end of the second stiffener 26 is connected to the batterycase 51 via the lower portion of the first stiffener 25, the lower wall22A of the inner panel 22, and the bracket 56. Therefore, the loadapplied to the lower portion of the second stiffener 26 at the time of aside crash is transmitted to the battery case 51 via the lower portionof the first stiffener 25, the lower wall 22A, and the bracket 56. Thisload transmission path is referred to as a second load transmissionpath. In other words, the second stiffener 26 can transmit a reactionforce from the battery case 51 via the second load transmission path atthe time of a side crash.

FIGS. 6 to 8 show the mode of deformation of the vehicle body structure1 when a vertically extending pole-like object 70 collides with the sidesill 2 from sideways (as is the case at the time of a side crash). Whenthe object 70 collides against the side sill 2 from the outboard side,the vertical wall lower portion 21G of the outer panel 21 that islocated in a most outboard part of the side sill 2 first collides withthe object 70. As shown in FIG. 6, the vertical wall lower portion 21Gdeforms inward upon receiving the load from the object 70, and hits thevertical wall 26C of the second stiffener 26. At this time, the secondstiffener 26 receives a reaction force from the front floor panel 18 andthe intermediate cross member 13 via the first load transmission path atthe upper end portion so that a reaction force from the battery case 51is transmitted to the lower end portion of the second stiffener 26 viathe second load transmission path. As a result, the second stiffener 26is compressed and deformed in the transverse direction between the outerpanel 21 and the first stiffener 25. At this time, the second stiffener26 deforms with each bending portion 31 acting as a starting point sothat the deformation of the second stiffener 26 occurs in apredetermined deformation mode. More specifically, the lower wall 26B ofthe second stiffener 26 is bent so as to protrude upward while the upperwall 26D is bent so as to protrude downward owing to the mutuallyopposing convex curvatures of the bending portions 31. As a result, thevertical wall 26C is caused to move strictly in the inboard directionwithout moving vertically so that the lower wall 26B and the upper wall26D of the second stiffener 26 are compressed in the transversedirection in a controlled manner. In particular, the second stiffener 26is prevented from moving (swinging) vertically, and is compressed in theinboard direction substantially along a linear path. The energy of theload is thus absorbed by the deformation of the second stiffener 26. Asthe second stiffener 26 is compressed, the parts of the lower wall 26Band the upper wall 26D located on either transverse side of the bendingportions 31 come into contact with each other in the transversedirection with the result that the reaction force starts increasingsharply, and the capability of the second stiffener 26 to transmit thereaction force sharply increases. In other words, a secondary crash thatoccurs to the lower wall 26B and the upper wall 26D causes the reactionforce to be transmitted in an efficient manner. Thereafter, the lowerwall 26B and the upper wall 26D are further compressed in the transversedirection and continue to transmit the reaction load. In this manner,the second stiffener 26 initially absorbs the energy of the side impact,and then starts transmitting the impact load in an efficient manner. Thebeads 26F increase the rigidity of the lower wall 26B and the upper wall26D, and can thereby increase the amount of energy that the secondstiffener 26 can absorb.

As the deformation of the second stiffener 26 progresses, as shown inFIG. 7, the third stiffener 27 and the side member 12 constituting thefirst load transmission path are deformed, and the front floor panel 18is deformed to absorb the energy of the impact. In addition, the lowerwall 22A of the inner panel 22 and the transverse wall portion 56B ofthe bracket 56 constituting the second load transmission path aredeformed so as to absorb the energy of the impact load. As the sidemember 12, the front floor panel 18, and the transverse wall portion 56Bof the bracket 56 are compressed in the transverse direction, the sidesill 2 moves in the inboard direction until the vertical wall lowerportion 22G abuts the vertical wall portion 56A of the bracket 56 andthe flanges 52B and 53B of the battery case 51. Further, the lowerflange 22D of the inner panel 22 abuts the outboard end of thetransverse wall portion 56B of the bracket 56. Subsequently, as shown inFIG. 8, the third stiffener 27, the lower wall 22A of the inner panel22, and the transverse wall portion 56B of the bracket 56 are interposedand compressed between the object 70 and the battery case 51 and/or thevertical wall portion 56A of the bracket 56. As a result, the energy ofthe impact load is thus further absorbed by the third stiffener 27, thelower wall 22A of the inner panel 22, and the transverse wall portion56B of the bracket 56 as the deformation of these components progressfurther. At this time, the battery case 51 may slightly deform under theload.

FIG. 9 shows an example for comparison. This vehicle body structure 1 issimilar to that of the illustrated embodiment, but lacks the bendingportions 31 in the second stiffener 26. When the bending portions 31 areomitted, there is no definite starting point of deformation in the lowerwall 26B and the upper wall 26D. The boundary between the lower wall 26Band the lower flange 26A and the boundary between the upper wall 26D andthe upper flange 26E are likely to be starting points of deformationowing to the sharp bends therein. As a result, the lower wall 26B andthe upper wall 26D of the second stiffener 26 tend to incline upward ordownward at the time of a side crash so that the lower wall 26B and theupper wall 26D do not undergo a compressive deformation. Therefore, theamount of energy absorbed by the second stiffener 26 under an impactload is substantially smaller than in the case of the illustratedembodiment where the bending portions 31 are provided. In addition, asthe second stiffener 26 tilts upward or downward as a whole, the amountof the load transmitted by the first load transmission path decreases,and a greater amount of load must be transmitted by the second loadtransmission path. As a result, the load applied to the battery case 51increases, and the amount of deformation of the battery case 51increases.

FIG. 10 is a graph showing the effect of the presence and absence of thebending portions 31 on the amount of deformation of the battery case 51.The horizontal axis represents the amount of the inboard movement of theobject 70, and the value is set to 0 when the object 70 comes intocontact with the side sill 2. The vertical axis represents thedeformation amount of the battery case 51, or more specifically, theamount of movement of the outer edge of the battery case 51 in theinboard direction. As shown in FIG. 10, the amount of deformation of thebattery case 51 when the bending portions 31 are provided is smallerthan in the case where the bending portions 31 are not provided. Thisresult is attributable to the fact that the amount of energy of theimpact load absorbed by the second stiffener 26 is relatively small inthe case of the example for comparison so that the load is applied tomainly via the second load transmission path, and the load applied tothe battery case 51 increases.

In the vehicle body structure 1 according to the present embodiment, thesecond stiffener 26 and the first stiffener 25 are connected to thefront floor panel 18 and the intermediate cross member 13 via the firstload transmission path including the third stiffener 27, the inner panel22 and the side member 12. As a result, at the time of a side crash, thesecond stiffener 26 and the first stiffener 25 receive a reaction forcefrom the front floor panel 18 and the intermediate cross member 13 viathe side member 12, the inner panel 22, and the third stiffener 27, andcan thereby deform in a predetermined way at the time of a side crash.Further, the second stiffener 26 and the first stiffener 25 areconnected to the battery case 51 via the second load transmission pathincluding the inner panel 22 and the bracket 56. As a result, the secondstiffener 26 and the first stiffener 25 receive a reaction force fromthe battery case 51 via the bracket 56 and the inner panel 22, and canthereby deform in a predetermined manner at the time of a side crash. Bythese means, the side sill 2 can efficiently absorb the energy of theside impact load.

Since the outer flange 27B which forms the outboard edge of the thirdstiffener 27 and the upper flange 26E which forms the upper edge of thesecond stiffener 26 laterally oppose each other via the first stiffener25, the third stiffener 27 is enabled to efficiently apply a reactionforce to the second stiffener 26 at the time of a side crash.

Since the inner flange 27C forming the inboard edge of the thirdstiffener 27 and the outer edge joining portion 12A forming the outboardedge of the side member 12 laterally oppose each other via the verticalwall intermediate portion 22H of the inner panel 22, the side member 12is enabled to efficiently apply a reaction force to the third stiffener27 at the time of a side crash.

Since the inboard edge of the lower wall 26B of the second stiffener 26and the lower wall 22A of the inner panel 22 oppose each other via thefirst stiffener 25, the lower wall 22A of the panel 22 is enabled toefficiently apply a reaction force to the second stiffener 26.

Since the flanges 52B and 53B of the battery case 51 extend in thehorizontal direction and are fastened to each other in an overlappingrelationship, the stiffness of the main bodies 52A and 53A against atransverse load is enhanced. Since the flanges 52B and 53B of thebattery case 51 are arranged at the same height as the inner flange 27Cforming the inboard edge of the third stiffener 27, the inner flange 27Cof the third stiffener 27 and the flanges 52B and 53B of the batterycase 51 are likely to oppose each other via the vertical wallintermediate portion 22H of the inner panel 22 at the time of a sidecrash. Therefore, the battery case 51 is enabled to efficiently apply areaction force to the third stiffener 27 via the inner panel 22 at theflanges 52B and 53B thereof. Further, since the battery case 51 abutsagainst the inner panel 22 at the flanges 52B and 53B having arelatively high rigidity than the main bodies 52A and 53A against atransverse load, the deformation of the battery case 51 can be minimizedat the time of a side crash.

Since the bracket 56 is provided with the vertical wall portion 56A andthe transverse wall portion 56B extending from the lower end of thevertical wall portion 56A in the outboard direction, an end of thebracket 56 can be joined to the lower wall 22A of the inner panel 22which is located adjacent to the lower end of the first stiffener 25while the bracket 56 is positioned transversely between the battery case51 and the side sill 2. As a result, the bracket 56 is enabled toefficiently apply a reaction force to the first stiffener 25 at the timeof a side crash. Further, as the side sill 2 moves in the inboarddirection at the time of a side crash, the bracket 56 is compressedbetween the side sill 2 and the battery case 51, and can thereby absorbthe energy of the impact load.

Since the bracket 56 has a lower rigidity than the battery case 51against a transverse loading, the bracket 56 deforms earlier than thebattery case 51 so as to absorb the energy of the impact load at thetime of a side crash. As a result, the deformation of the battery case51 can be minimized.

In the vehicle body structure 1 according to the present embodiment, thedoor slide rail 35 and the rail case 36 can be positioned in an upperpart of the side sill 2. The door slide rail 35 and the rail case 36 arepositioned above the first to third stiffeners 25 to 27 for absorbingthe energy of the impact load at the time of a side crash. Thus, thevehicle body structure 1 according to the present embodiment canfavorably absorb the energy of an impact load of a side crash eventhough the door slide rail 35 and the rail case 36 are provided in theside sill 2.

Although the present invention has been described in terms of a specificembodiment, the present invention is not limited by such an embodiment,but can be modified and altered in various ways without departing fromthe spirit of the present invention.

The invention claimed is:
 1. A vehicle body structure, comprising: apair of side sills extending in a fore and aft direction along eitherlower side part of a vehicle body; a pair of brackets joined to inboardsides of the respective side sills; and a battery case joined to thebrackets and receiving a battery pack therein; wherein each side sillincludes: an outer panel formed as a channel member extending in thefore and aft direction and having an open side facing in an inboarddirection; an inner panel formed as a channel member extending in thefore and aft direction and having an open side facing in an outboarddirection, the outer panel and the inner panel being joined to eachother at upper and lower edges thereof; a first stiffener extending inthe fore and aft direction in a space defined between the outer paneland the inner panel and having a lower edge joined to the lower edges ofthe outer panel and the inner panel; and a second stiffener formed as achannel member extending in the fore and aft direction and having anopen side facing in the inboard direction, the second stiffener havingan upper edge and a lower edge attached to an outboard side of the firststiffener, wherein the second stiffener includes a second stiffenerlower wall extending in the outboard direction from the upper edge ofthe lower edge of the second stiffener, and a second stiffener upperwall extending in the outboard direction from the upper edge of thesecond stiffener, and the second stiffener lower wall and the secondstiffener upper wall are formed with at least one bending portion bentinward of the channel shape defined by the second stiffener.
 2. Thevehicle body structure according to claim 1, wherein the outer panelincludes: an outer lower wall extending transversely, an outer verticalwall extending upward from an outboard edge of the outer lower wall, anouter upper wall extending in the inboard direction from an upper edgeof the outer vertical wall, an outer lower flange extending downwardfrom an inboard edge of the outer lower wall, and an outer upper flangeextending upward from an inboard edge of the outer upper wall, whereinthe inner panel includes: an inner lower wall extending transversely, aninner vertical wall extending upward from an inboard edge of the innerlower wall, an inner upper wall extending in the outboard direction froman upper edge of the inner vertical wall, an inner lower flangeextending downward from an outboard edge of the inner lower wall andjoined to the outer lower flange, and an inner upper flange extendingupward from an outboard edge of the inner upper wall and joined to theouter upper flange, and wherein the second stiffener includes: a secondstiffener lower flange joined to the first stiffener, a second stiffenervertical wall extending upward from an outboard edge of the secondstiffener lower wall, and a second stiffener upper flange extendingupward from an inboard edge of the second stiffener upper wall andjoined to the first stiffener, an outboard edge of the inner lower wallbeing offset upward from an inboard edge of the outer lower wall, andtransversely opposing an inboard edge of the second stiffener lower wallvia the first stiffener, the second stiffener lower wall extending inthe outboard direction from an upper edge of the second stiffener lowerflange, and the second stiffener upper wall extending in the inboarddirection from an upper edge of the second stiffener vertical wall. 3.The vehicle body structure according to claim 2, wherein the batterycase includes a lower case having an opening facing upward and a flangeextending along a periphery of the opening, and an upper case closingthe opening of the lower case and having a periphery joined to theflange of the lower case, the battery case being joined to the bracketsat the flange of the lower case.
 4. The vehicle body structure accordingto claim 3, wherein each bracket includes a vertical wall portionextending downward from the flange of the lower case, and a transversewall portion extending from a lower end of the vertical wall portion tounder the inner lower wall to be joined to the inner lower wall.
 5. Thevehicle body structure according to claim 4, wherein each bracket has alower rigidity than the lower case against a transverse loading.
 6. Thevehicle body structure according to claim 2, wherein the inner lowerwall is provided with a plurality of beads each extending in atransverse direction.
 7. The vehicle body structure according to claim2, further comprising a third stiffener extending in the fore and aftdirection in a space defined between the inner lower wall and the innerupper wall, and in a transverse direction to have an outboard edgejoined to the first stiffener and an inboard edge joined to the innervertical wall.
 8. The vehicle body structure according to claim 7,wherein the outboard edge of the third stiffener and the upper edge ofthe second stiffener transversely oppose each other via the firststiffener.
 9. The vehicle body structure according to claim 7, furthercomprising a floor panel having a vertically facing surface and attachedto upper sides of the inner upper walls along respective lateral sideedges thereof; and a pair of side members each having an outboard edgeattached to an inboard side of the inner vertical wall and an inboardedge attached a lower surface of the floor panel.
 10. The vehicle bodystructure according to claim 9, further comprising a cross memberextending transversely and attached to the lower surface of the floorpanel, two transverse ends of the cross member being joined to therespective side members.
 11. The vehicle body structure according toclaim 2, wherein a lower edge of the first stiffener is provided with aplurality of notches extending upward, and the outer lower flange, thesecond stiffener lower flange, a lower edge of the first stiffener, andthe inner lower flange are laid over one another, and the outer lowerflange, the second stiffener lower flange, and the inner lower flangeare integrally welded to one another at positions corresponding to thenotches.
 12. The vehicle body structure according to claim 1, furthercomprising a door slide rail provided between the inner panel and theouter panel, and located above the first stiffener, the door slide railbeing configured to slidably guide a lower end of a slide door.
 13. Avehicle body structure, comprising: a pair of side sills extending in afore and aft direction along either lower side part of a vehicle body; apair of brackets joined to inboard sides of the respective side sills;and a battery case joined to the brackets and receiving a battery packtherein; wherein each side sill includes: an outer panel formed as achannel member extending in the fore and aft direction and having anopen side facing in an inboard direction; an inner panel formed as achannel member extending in the fore and aft direction and having anopen side facing in an outboard direction, the outer panel and the innerpanel being joined to each other at upper and lower edges thereof; afirst stiffener extending in the fore and aft direction in a spacedefined between the outer panel and the inner panel and having a loweredge joined to the lower edges of the outer panel and the inner panel;and a second stiffener formed as a channel member extending in the foreand aft direction and having an open side facing in the inboarddirection, the second stiffener having an upper edge and a lower edgeattached to an outboard side of the first stiffener, wherein the innerpanel includes an inner lower wall extending transversely, and the innerlower wall is provided with a plurality of beads each extending in atransverse direction.
 14. A vehicle body structure, comprising: a pairof side sills extending in a fore and aft direction along either lowerside part of a vehicle body; a pair of brackets joined to inboard sidesof the respective side sills; and a battery case joined to the bracketsand receiving a battery pack therein; wherein each side sill includes:an outer panel formed as a channel member extending in the fore and aftdirection and having an open side facing in an inboard direction; aninner panel formed as a channel member extending in the fore and aftdirection and having an open side facing in an outboard direction, theouter panel and the inner panel being joined to each other at upper andlower edges thereof; a first stiffener extending in the fore and aftdirection in a space defined between the outer panel and the inner paneland having a lower edge joined to the lower edges of the outer panel andthe inner panel; and a second stiffener formed as a channel memberextending in the fore and aft direction and having an open side facingin the inboard direction, the second stiffener having an upper edge anda lower edge attached to an outboard side of the first stiffener,wherein the inner panel includes an inner lower wall extendingtransversely, an inner vertical wall extending upward from an inboardedge of the inner lower wall, an inner upper wall extending in theoutboard direction from an upper edge of the inner vertical wall, andwherein the vehicle body structure further comprises a third stiffenerextending in the fore and aft direction in a space defined between theinner lower wall and the inner upper wall, and in a transverse directionto have an outboard edge joined to the first stiffener and an inboardedge joined to the inner vertical wall.